1. Field of the Invention
This invention relates to polyimide excelling in heat resistance, chemical resistance, water repellency, dielectric characteristics, electrical characteristics, and optical characteristics, polyamide acid useful as a precursor therefor, and an optical material formed by using the polyimide.
2. Description of the Related Art
The electronics industry as a key industry in the computer and information society is now prospering immensely. The role manifested by polymeric materials in the progress of the electronics technology is truly preeminent. But for the polymeric materials intended for insulation and for fine processing, the electronics age of today would not have been realized. When the polymeric materials which are mainly characterized by their ability to inhibit the flow of electricity are allowed to have their constructions of molecules and aggregates conditioned adequately, they are enabled to manifest such functions as ferroelectricity, high electronic and ionic conductivity, superconductivity, and ferromagnetism as well which have been heretofore held as characteristics of metals, semiconductors, and even inorganic materials. In recent years, therefore, the researches of polymers as electronically functional materials have been greatly expanding their domains. These polymers have been finding utility for various applications such as, for example, layer insulating films and passivation materials for transistors, thyristors, and ICs, junction coating represented by silicone resins, tippy coat grade buffer for relaxing mold stress, .-ray shielding materials for coping with the soft errors in memory elements, die bonding materials, resist materials, semiconductor sealing materials, moisture-proof coating materials for hybrid ICs, TAB (tape automated bonding) grade chip carrier tapes, and multilayer circuit boards.
Among these polymeric materials enumerated above, the polyimide has attracted attention particularly on account of its excellent functions and heat resistance and has incited enthusiastic researches and developments. At present, applications of the polyimide to such usage as mentioned above are attempted actively. JP-A-05-1148, for example, discloses a perfluorinated polyimide that is composed of repeating units exclusively containing a carbon-fluorine bond (C—F bond) instead of a carbon-hydrogen bond (C—H bond). This polyimide indeed possesses sufficient heat resistance for manufacture of a optoelectronic integrated circuit and incurs light transmission loss only very slightly in the wavelength of near-infrared ray, particularly in the wavelength of light communication (1.0-1.7 μm). Notwithstanding this fact, the optical waveguide or the optical fiber core clad which is produced with the aforementioned combination of materials exhibits a refractive index difference, .n, of about 0.2% and fails to offer a sufficiently practicable refractive index difference of not less than 0.5%.
Besides, the polyimide which excels in heat resistance, chemical resistance, water repellency, dielectric characteristics, electrical characteristics, and optical characteristics as mentioned above is strongly demanded and nevertheless has not existed to date. Thus, this invention has been initiated in view of this affairs and is directed toward providing a polyimide excelling in heat resistance, chemical resistance, water repellency, dielectric characteristics, electrical characteristics, and optical characteristics and exhibiting a refractive index difference, .n, exceeding 0.5% relative to the existing perfluorinated polyimide and providing a polyamide acid useful as the raw material for the polyimide.
The other object of this invention is to provide optical materials using the polyimide.